Caffeine May Leave People More Open to Persuasion, Study Shows

Caffeine May Leave People More Open to Persuasion, Study Shows
By Miranda Hitti
WebMD Medical News Reviewed By Louise Chang, MD
on Monday, June 05, 2006

June 5, 2006 -- Planning to ask your boss for a raise? You might want to do it over a cup of coffee.

A new study reports people may be more easily persuaded to change their opinion after consuming caffeine.

Researchers in Brisbane, Australia found undistracted university students were more persuaded by arguments made after they drank a caffeine-laced drink.

Caffeine has been shown to boost attention. But few studies have checked caffeine's effects on persuasiveness, note Pearl Martin, PhD, and colleagues. Martin works at the University of Queensland's School of Psychology.

Caffeine is found in coffee, tea, some soft drinks, and other products. It's often consumed in settings that could involve "persuasive communication," note Martin and colleagues.

For instance, people might drink coffee while reading the newspaper or watching TV.

"The practical implications of our findings to 'real world' settings are many and therefore warrant future investigation," the researchers write in the European Journal of Social Psychology.
Caffeine Study

Martin's study included 120 university students, half of whom were women.

First, the students took surveys about their views on a controversial topic. For men, the topic was abortion. For women, it was euthanasia, defined in the study as a person's right to end his life if he has a terminal illness.

Later, researchers served orange juice to the students. Some got plain orange juice, which has no caffeine. The others got juice with caffeine added.

The students didn't know which they received. They had previously been asked not to consume caffeine or alcohol, beginning the night before the experiment.

None of the students was pregnant, a smoker, or a heavy user of caffeine.

Making the Case

The researchers told the students to drink the orange juice quickly. The experiment began 40 minutes after they had finished the drink in order to allow the caffeine to take its full effect.

Next, researchers gave the students publications to read which made points counter to their opinions on abortion or euthanasia. Men received the abortion publication; women the one about euthanasia.

Some students were told to pay close attention to the points made in the publication. Others were given a distracting task, such as crossing out the letter "o" throughout the text.

Afterwards, all students rated how much -- if at all -- their opinions had changed. The point was to see if caffeine and distractions affected persuasiveness.

Open to Persuasion

Students who drank the caffeine-laced juice were more apt to be persuaded by the publications, the study shows.

But there was a catch. Those who had done the distracting task stuck with their original opinion, even if they'd had the caffeinated orange juice.

Caffeine may have made students more likely to change their minds, but only if they weren't distracted.

It's not clear why caffeine increased persuasiveness. Maybe caffeine affected how the students processed the message. Or perhaps caffeine upped emotional arousal and/or improved mood, making the students more likely to agree with the message, the researchers note.